Mercia

Mercia was an Anglo-Saxon kingdom in England which existed from 527 to 918, with Tamworth serving as its capital. In 584, Creoda of Mercia built a fortress at Tamworth which became the seat of Mercia's kings, and it was centered on the valley of the River Trent and its tributaries in the Midlands. Between 600 and 900, it annexed East Anglia, Sussex, Essex, Kent, and Wessex, and it dominated England south of the River Humber. During the late 7th century, the Mercians adopted Christianity. During the early 9th century, Wessex surpassed Mercia as the most powerful Anglo-Saxon kingdom. During the Viking invasions of England, Mercia relied upon West Saxon support to save it from the Great Heathen Army, and the Viking puppet king Ceolwulf II of Mercia's death in 879 led to Alfred the Great's vassal and son-in-law Aethelred of Mercia rising to the throne. Aethelred died in 910, and his able wife Aethelflaed succeeded him as ruler of Mercia, expanding it in alliance with Wessex. During her rule, Mercia reconquered its whole pre-865 kingdom, but, upon her death in 918, King Edward the Elder of Wessex had her daughter Aelfwynn of Mercia confined to a monastery as he annexed Mercia to Wessex.